In conventional power-generation control systems for motor vehicles, an IC regulator is operative to adjust an output voltage of an engine-driven alternator to a target voltage. The adjusted output voltage is supplied to a battery and vehicle electrical loads. The target voltage is determined depending on the operating conditions of the engine and/or various power requirements of the vehicle electrical loads.
When a battery voltage is changed to be unmatched with the target voltage, a corrected value is supplied from an engine ECU (Electronic Control Unit) to the IC regulator so that the corrected value is added to the target voltage so as to match the target voltage with the battery voltage.
In the alternator voltage control set forth above, in order to find faults of the power-generation control system, an example of malfunction determining methods is disclosed in Japanese Unexamined Patent Publication H08-079981.
The method disclosed in the JP Unexamined Patent Publication is designed to monitor the corrected value to be supplied from the engine ECU to the IC regulator and to determine that any failure occurs in a power-generation control system when the monitored corrected value exceeds a predetermined threshold value.
Specifically, the conventional method set forth above continuously compares the target voltage with an actual output voltage of the alternator, calculates the corrected value for the target voltage based on the comparison result, and monitors the calculated corrected value.
In conventional IC regulators, an example of malfunction determining methods is disclosed in U.S. Pat. No. 5,703,472 corresponding to Japanese Unexamined Patent Publication No. H09-019080.
In the method disclosed in the US Patent Publication, a voltage of a communication terminal of an IC regulator connected with an outside control unit, such as an ECU, via a communication line is set to a predetermined voltage. A voltage of a signal to be input to the communication terminal of the IC regulator is monitored, and the monitored voltage is compared with a specific voltage range.
When the monitored voltage is out of the specific voltage range, it is possible to determine that at least one of abnormalities occurs in the communication line; these abnormalities include a break or a short in the communication line and a short of the communication line to a positive or negative terminal of a battery. This makes it possible to control an output voltage of an alternator to thereby protect the battery and/or electrical loads connected with the battery.
In addition, U.S. Pat. No. 7,183,750 B2 corresponding to Japanese Unexamined Patent Publication No. 2006-115619 discloses a method of maintaining proper power-generation control even if a wrong command signal specifying a target voltage is input to an IC regulator.
Specifically, in the method disclosed in the U.S. Pat. No. 7,183,750 B2, an output voltage of an engine-driven alternator is monitored whether it lies within a predetermined proper range. When it is monitored that the alternator output voltage becomes out of the predetermined proper range based on the monitor result, it is determined that the command signal specifying the target voltage becomes wrong. At the time of the wrong target-voltage determination, a preset target voltage maintained within the predetermined voltage range is used to adjust the alternator output voltage.